The central hypertensive effects induced by
bradykinin are known to be mediated via B2 receptors, which are present constitutively in the brain. B, receptors are rapidly upregulated during
inflammation,
hyperalgesia, and experimental diabetes. The hypothalamus plays an important role in the regulation of cardiovascular homeostasis, and all components of kallikrein-kinin system have been identified in this area. Therefore, we analyzed the
mRNA expression of B1 and B2 receptors in the hypothalamus of spontaneously hypertensive rats (SHR) by RT-PCR. Male SHR were studied at three different ages corresponding to the three phases in the development of
hypertension: (i) 3-4 (prehypertensive), (ii) 7-8 (onset of
hypertension), and (iii) 12-13 weeks (established
hypertension) after birth, and compared with age-matched Wistar-Kyoto (WKY) rats. At all ages tested, B2 receptor
mRNA levels in the hypothalamus of SHR were higher than age-matched WKY rats (p < 0.001). However, the B1 receptor
mRNA levels were higher at the established phase of
hypertension only. We conclude that B1 and B2 receptor
mRNA are differentially expressed in the hypothalamus of SHR and may play different roles in the pathogenesis of
hypertension: upregulation of B2 receptor
mRNA from early age may participate in the pathogenesis of
hypertension, whereas an upregulation of B1 receptor
mRNA in the established phase of
hypertension may reflect an epiphenomenon in
essential hypertension.